This invention relates generally to glass-ceramic cooktop appliances and more particularly to contact sensing approaches for such appliances.
The use of glass-ceramic plates as cooktops in cooking appliances is well known. Such cooking appliances (referred to herein as glass-ceramic cooktop appliances) typically include a number of heating units mounted under the glass-ceramic plate and a controller for controlling the power applied to the heating units. The glass-ceramic plate presents a pleasing appearance and is easily cleaned in that the smooth, continuous surface prevents spillovers from falling onto the heating units underneath the cooktop.
In one known type of glass-ceramic cooktop appliance, the glass-ceramic plate is heated by radiation from a heating unit, such as an electric coil or a gas burner, disposed beneath the plate. The glass-ceramic plate is sufficiently heated by the heating unit to heat utensils upon it primarily by conduction from the heated glass-ceramic plate to the utensil. Another type of glass-ceramic cooktop appliance uses a heating unit that radiates substantially in the infrared region in combination with a glass-ceramic plate that is substantially transparent to such radiation. In these appliances, a utensil placed on the cooktop is heated primarily by radiation transmitted directly from the heating unit to the utensil, rather than by conduction from the glass-ceramic plate. Such radiant glass-ceramic cooktops are more thermally efficient than other glass-ceramic cooktops and have the further advantage of responding more quickly to changes in the power level applied to the heating unit. Yet another type of glass-ceramic cooktop appliance inductively heats utensils placed on the cooking surface. In this case, the energy source is an RF generator that emits RF energy when activated. The utensil, which comprises an appropriate material, absorbs the RF energy and is thus heated.
In each type of glass-ceramic cooktop appliances, provision must be made to avoid overheating the glass-ceramic plate. For most glass-ceramic materials, the operating temperature should not exceed 600-700xc2x0 C. for any prolonged period. Under normal operating conditions, the temperature of the glass-ceramic plate will generally remain below this limit. However, conditions can occur during operation that can cause this temperature limit to be exceeded. Commonly occurring examples include operating the appliance with a small load or no load (i.e., no utensil) on the cooking surface, using badly warped utensils that make uneven contact with the cooking surface, and operating the appliance with a shiny and/or empty utensil.
To protect the glass-ceramic from extreme temperatures, glass-ceramic cooktop appliances ordinarily have some sort of temperature sensing device that can cause the heating unit to be shut down if high temperatures are detected. In addition to providing thermal protection, such temperature sensors can be used to provide temperature-based control of the cooking surface and to provide a hot surface indication, such as a warning light, after a burner has been turned off. Temperature sensing can also be used to detect other cooktop related properties such as the presence or absence of a utensil on the cooktop, the temperature, size or type of utensil on the cooktop, or properties, such as boiling state, of the utensil contents.
One common approach to sensing temperature in glass-ceramic cooktop appliances is to place a temperature sensor directly on the underside of the glass-ceramic plate. With this approach, however, the temperature sensor is subject to the high burner temperatures and thus more susceptible to failure. Furthermore, direct contact sensors are normally in the form of traces that are pasted directly to the underside of the glass-ceramic plate. Pasting traces to the glass-ceramic plate is a difficult, expensive process, and if a trace fails in any manner, the entire glass-ceramic plate needs to be replaced. In light of these issues, most cooktop sensor configurations in use today employ an optical sensor assembly that xe2x80x9clooksxe2x80x9d at the glass-ceramic surface from a remote location to detect the temperature and other cooktop properties. While remote optical sensing generally functions well, it typically requires guide optics that add to the overall cost of the sensor assembly.
Accordingly, it would be desirable to have effective and cost efficient glass-ceramic sensing arrangements that utilize direct contact sensors.
The above-mentioned need is met by the present invention, which provides a glass-ceramic cooktop appliance having at least one burner assembly disposed under a glass-ceramic plate. The cooktop appliance includes a sensor assembly having a support bar mounted on the burner assembly adjacent to the glass-ceramic plate and a means for sensing cooktop related properties mounted on the support bar so as to be in contact with the glass-ceramic plate.
The present invention and its advantages over the prior art will become apparent upon reading the following detailed description and the appended claims with reference to the accompanying drawings.